U.S. patent application number 10/404981 was filed with the patent office on 2004-09-30 for arangements of microstrip antennas having dielectric substrates including meta-materials.
Invention is credited to Delgado, Heriberto Jose, Killen, William D., Plke, Randy T..
Application Number | 20040189528 10/404981 |
Document ID | / |
Family ID | 32990233 |
Filed Date | 2004-09-30 |
United States Patent
Application |
20040189528 |
Kind Code |
A1 |
Killen, William D. ; et
al. |
September 30, 2004 |
ARANGEMENTS OF MICROSTRIP ANTENNAS HAVING DIELECTRIC SUBSTRATES
INCLUDING META-MATERIALS
Abstract
A slot fed microstrip patch antenna (300) includes a conducting
ground plane (308), the conducting ground plane (308) including at
least one slot (306). A dielectric material is disposed between the
ground plane (308) and at least one feed line (317), wherein at
least a portion of the dielectric layer (313) includes magnetic
particles (324). The dielectric layer between the feed line (317)
and the ground plane (308) provides regions having high relative
permittivity (313) and low relative permittivity (312). At least a
portion of the stub (318) is disposed on the high relative
permittivity region (313).
Inventors: |
Killen, William D.;
(Melbourne, FL) ; Plke, Randy T.; (Grant, FL)
; Delgado, Heriberto Jose; (Melbourne, FL) |
Correspondence
Address: |
SACCO & ASSOCIATES, PA
P.O. BOX 30999
PALM BEACH GARDENS
FL
33420-0999
US
|
Family ID: |
32990233 |
Appl. No.: |
10/404981 |
Filed: |
March 31, 2003 |
Current U.S.
Class: |
343/700MS |
Current CPC
Class: |
H01Q 9/0457
20130101 |
Class at
Publication: |
343/700.0MS |
International
Class: |
H01Q 001/38 |
Claims
What is claimed is:
1. A slot fed microstrip patch antenna, comprising: an electrically
conducting ground plane, said ground plane having at least one
slot; a feed line for transferring signal energy to or from said
slot, said feed line including a stub which extends beyond said
slot; a first dielectric layer disposed between said feed line and
said ground plane, said first dielectric layer having a first set
of dielectric properties including a first relative permittivity
over a first region, and at least a second region of said first
dielectric layer having a second set of dielectric properties, said
second set of dielectric properties providing a higher relative
permittivity as compared to said first relative permittivity,
wherein said stub is disposed on said second region, and at least
one patch radiator and a second dielectric layer, said second
dielectric layer disposed between said ground plane and said patch
radiator, wherein said second dielectric layer includes a third
region providing a third set of dielectric properties including a
third relative permittivity, and at least a fourth region including
a fourth set of dielectric properties, said fourth set of
dielectric properties including a higher relative permittivity as
compared to said third relative permittivity.
2. The antenna of claim 1, wherein said patch is disposed on said
fourth region.
3. The antenna of claim 1, wherein at least one of said first and
second dielectric layer comprises a ceramic material, said ceramic
material having a plurality of voids, at least a portion of said
voids filled with magnetic particles.
4. The antenna of claim 3, wherein said magnetic particles comprise
meta-materials.
5. The antenna of claim 2, wherein an intrinsic impedance in a
first junction region between said feed line and said slot is
matched to said fourth region.
6. The antenna of claim 2, wherein an intrinsic impedance in a
first junction region between said feed line and said slot is
matched to an intrinsic impedance of said second region.
7. The antenna of claim 5, wherein an intrinsic impedance of said
first junction region is matched to an intrinsic impedance of said
second region.
8. The antenna of claim 1, wherein said at least a first patch
radiator comprises a first and a second patch radiator, said first
and said second patch radiators separated by a third dielectric
layer.
9. The antenna of claim 8, wherein said second patch radiator is
disposed on a dielectric region in said third dielectric layer
having magnetic particles.
10. The antenna of claim 1, wherein said first dielectric provides
a quarter wavelength matching section proximate to said slot to
match said feed line into said slot.
11. The antenna of claim 10, wherein said quarter wave matching
section includes magnetic particles.
12. The antenna of claim 1, wherein said slot comprises at least
one crossed slot and said feed line comprises at least two feed
lines, said feed lines phased to provide a dual polarization
emission pattern.
13. A slot fed microstrip antenna, comprising: an electrically
conducting ground plane, said ground plane having at least one
slot; a first dielectric layer disposed on said ground plane, and
at least one feed line disposed on said first dielectric material
for transferring signal energy to or from said slot, said feed line
including a stub portion, wherein said first dielectric layer
includes a plurality of magnetic particles, at least a portion of
said magnetic particles being disposed in a first junction region
between said feed line and said slot, said first dielectric layer
having a first relative permittivity over a first region and a
second relative permittivity over a second region, said second
region having a higher relative permittivity as compared to said
first region, wherein at least a portion of said stub is disposed
on said second region.
14. The antenna of claim 13, wherein said first dielectric layer
comprises a ceramic material, said ceramic material having a
plurality of voids, at least some of said voids filled with
magnetic particles.
15. The antenna of claim 14, wherein said magnetic particles
comprise meta-materials.
16. The antenna of claim 13, wherein said second region includes
magnetic particles.
17. The antenna of claim 13, wherein an intrinsic impedance in said
first junction region is matched to said second region.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Statement of the Technical Field
[0002] The inventive arrangements relate generally slot
antennas.
[0003] 2. Description of the Related Art
[0004] RF circuits, transmission lines and antenna elements are
commonly manufactured on specially designed substrate boards.
Conventional circuit board substrates are generally formed by
processes such as casting or spray coating which generally result
in uniform substrate physical properties, including the dielectric
constant.
[0005] For the purposes RF circuits, it is generally important to
maintain careful control over impedance characteristics. If the
impedance of different parts of the circuit do not match, signal
reflections and inefficient power transfer can result. Electrical
length of transmission lines and radiators in these circuits can
also be a critical design factor.
[0006] Two critical factors affecting circuit performance relate to
the dielectric constant (sometimes referred to as the relative
permittivity or .epsilon..sub.r) and the loss tangent (sometimes
referred to as the dissipation factor or .delta.) of the dielectric
substrate material. The dielectric constant determines the
electrical wavelength in the substrate material, and therefore the
electrical length of transmission lines and other components
disposed on the substrate. The loss tangent determines the amount
of signal loss that occurs for signals traversing the substrate
material. Losses tend to increase with increases in frequency.
Accordingly, low loss materials become even more important with
increasing frequency, particularly when designing receiver front
ends and low noise amplifier circuits.
[0007] Printed transmission lines, passive circuits and radiating
elements used in RF circuits are typically formed in one of three
ways. One configuration known as microstrip, places the signal line
on a board surface and provides a second conductive layer, commonly
referred to as a ground plane. A second type of configuration known
as buried microstrip is similar except that the signal line is
covered with a dielectric substrate material. In a third
configuration known as stripline, the signal line is sandwiched
between two electrically conductive (ground) planes.
[0008] In general, the characteristic impedance of a parallel plate
transmission line, such as stripline or microstrip line, is
approximately equal to {square root}{square root over
(L.sub.l/C.sub.l)}, where L.sub.l is the inductance per unit length
and C.sub.l is the capacitance per unit length. The values of
L.sub.l and C.sub.l are generally determined by the physical
geometry and spacing of the line structure as well as the
dielectric constant of the dielectric material(s) used to separate
the transmission lines.
[0009] In conventional RF designs, a substrate material is selected
that has a single dielectric constant and relative permeability
value, the relative permeability value being about 1. Once the
substrate material is selected, the line characteristic impedance
value is generally exclusively set by controlling the geometry of
the line, the slot, and coupling characteristics of the line and
the slot.
[0010] Radio frequency (RF) circuits are typically embodied in
hybrid circuits in which a plurality of active and passive circuit
components are mounted and connected together on a surface of an
electrically insulating board substrate, such as a ceramic
substrate. The various components are generally interconnected by
printed metallic conductors, such as copper, gold, or tantalum,
which generally function as transmission lines (e.g. stripline or
microstrip line or twin-line) in the frequency ranges of
interest.
[0011] The dielectric constant of the selected substrate material
for a transmission line, passive RF device, or radiating element
determines the physical wavelength of RF energy at a given
frequency for that structure. One problem encountered when
designing microelectronic RF circuitry is the selection of a
dielectric board substrate material that is reasonably suitable for
all of the various passive components, radiating elements and
transmission line circuits to be formed on the board.
[0012] In particular, the geometry of certain circuit elements may
be physically large or miniaturized due to the unique electrical or
impedance characteristics required for such elements. For example,
many circuit elements or tuned circuits may need to have an
electrical length of a quarter of a wavelength. Similarly, the line
widths required for exceptionally high or low characteristic
impedance values can, in many instances, be too narrow or too wide
for practical implementation for a given substrate. Since the
physical size of the microstrip line or stripline is inversely
related to the dielectric constant of the dielectric material, the
dimensions of a transmission line or a radiator element can be
affected greatly by the choice of substrate board material.
[0013] Still, an optimal board substrate material design choice for
some components may be inconsistent with the optimal board
substrate material for other components, such as antenna elements.
Moreover, some design objectives for a circuit component may be
inconsistent with one another. For example, it may be desirable to
reduce the size of an antenna element. This could be accomplished
by selecting a board material with a high dielectric constant with
values such as 50 to 100. However, the use of a dielectric with a
high dielectric constant will generally result in a significant
reduction in the radiation efficiency of the antenna.
[0014] Antenna elements are sometimes configured as microstrip slot
antennas. Microstrip slot antennas are useful antennas since they
generally require less space, are simpler and are generally less
expensive to manufacture as compared to other antenna types. In
addition, importantly, microstrip slot antennas are highly
compatible with printed-circuit technology.
[0015] One factor in constructing a high efficiency microstrip slot
antenna is minimizing the power loss, which may be caused by
several factors including dielectric loss. Dielectric loss is
generally due to the imperfect behavior of bound charges, and
exists whenever a dielectric material is placed in a time varying
electromagnetic field. The dielectric loss, often referred as loss
tangent, is directly proportional to the conductivity of the
dielectric medium. Dielectric loss generally increases with
operating frequency.
[0016] The extent of dielectric loss for a particular microstrip
slot antenna is primarily determined by the dielectric constant of
the dielectric space between the radiator antenna element (e.g.,
slot) and the feed line. Free space, or air for most purposes, has
a relative dielectric constant and relative permeability
approximately equal to one.
[0017] A dielectric material having a relative dielectric constant
close to one is considered a "good" dielectric material as a good
dielectric material exhibits low dielectric loss at the operating
frequency of interest. When a dielectric material having a relative
dielectric constant substantially equal to the surrounding
materials is used, the dielectric loss due to impedance mismatches
is effectively eliminated. Therefore, one method for maintaining
high efficiency in a microstrip slot antenna system involves the
use of a material having a low relative dielectric constant in the
dielectric space between the radiator antenna slot and the
microstrip feed line exciting the slot.
[0018] Furthermore, the use of a material with a lower dielectric
constant permits the use of wider transmission lines that, in turn,
reduce conductor losses and further improve the radiation
efficiency of the microstrip slot antenna. However, the use of a
dielectric material having a low dielectric constant can present
certain disadvantages, such as the large size of the slot antenna
fabricated on a low dielectric constant substrate as compared to a
slot antenna fabricated on a high dielectric constant
substrate.
[0019] The efficiency of microstrip slot antennas is compromised
through the selection of a particular dielectric material for the
feed which has a single uniform dielectric constant. A low
dielectric constant is helpful in allowing wider feed lines, that
result in a lower resistive loss, to the minimization of the
dielectric induced line loss, and the minimization of the slot
radiation efficiency. However, available dielectric materials when
placed in the junction region between the slot and the feed result
in reduced antenna radiation efficiency due to the poor coupling
characteristics through the slot.
[0020] A tuning stub is commonly used to tune out the excess
reactance in microstrip slot antennas. However, the impedance
bandwidth of the stub is generally less than both the impedance
bandwidth of the radiator and the impedance bandwidth of the slot.
Therefore, although conventional stubs can generally be used to
tune out excess reactance of the antenna circuit, the low impedance
bandwidth of the stub generally limits the performance of the
overall antenna circuit.
SUMMARY OF THE INVENTION
[0021] A slot fed microstrip patch antenna includes an electrically
conducting ground plane having at least one slot and a feed line
for transferring signal energy to or from the slot. The feed line
includes a stub which extends beyond the slot. A first dielectric
layer is disposed between the feed line and the ground plane. T he
first dielectric layer has a first set of dielectric properties
including a first relative permittivity over a first region, and at
least a second region having a second set of dielectric properties.
The second set of dielectric properties provide a higher relative
permittivity as compared to the first relative permittivity,
wherein the stub is disposed on the higher permittivity second
region. At least one patch radiator is disposed on a second
dielectric layer, the second dielectric layer including a third
region providing a third set of dielectric properties including a
third relative permittivity, and at least a fourth region including
a fourth set of dielectric properties, the fourth set of dielectric
properties including a higher relative permittivity as compared to
the third relative permittivity. The patch is preferably disposed
on the fourth region.
[0022] The respective dielectric layers can comprise a ceramic
material having a plurality of voids, where at least a portion of
the voids are filled with magnetic particles. The magnetic
particles can comprise meta-materials.
[0023] The intrinsic impedance in a first junction region disposed
between the feed line and slot can be matched to the fourth region.
The intrinsic impedance in the first junction region can also be
matched to an intrinsic impedance of the second region which
underlies the stub. The intrinsic impedance of the first junction
region can be matched to both the intrinsic impedance of the second
region and the fourth region.
[0024] As used herein, the phrase "intrinsic impedance matched"
refers to an impedance match which is improved as compared to the
intrinsic impedance matching that would result given the respective
actual permittivity values of the regions comprising the interface,
but assuming the relative permeabilities to be 1 for each of the
respective regions. As noted earlier, prior to the invention,
although board substrates provided a choice regarding a single
relative permittivity value, the relative permeability of the board
substrates available was necessarily equal nearly 1.
[0025] The antenna can comprise a first and a second patch radiator
separated by a third dielectric layer. The second patch radiator is
preferably disposed on a dielectric region in the third dielectric
layer having magnetic particles.
[0026] The first dielectric can provide a quarter wavelength
matching section proximate to the slot to match the feed line into
the slot. The quarter wave matching section can include magnetic
particles.
[0027] The slot can comprise at least one east one crossed slot and
the feed line comprise at least two feed lines, the feed lines
phased to provide a dual polarization emission pattern.
[0028] A slot fed microstrip antenna includes an electrically
conducting ground plane including at least one slot, a first
dielectric layer disposed on the ground plane, and at least one
feed line disposed on the first dielectric material for
transferring signal energy to or from the slot. The feed line
includes a stub portion, wherein the first dielectric layer
includes a plurality of magnetic particles, at least a portion of
the magnetic particles being disposed in a first junction region
between the feed line and the slot. The first dielectric layer
provides a first relative permittivity over a first region and a
second relative permittivity over a second region, the second
region having a higher relative permittivity as compared to the
first region, wherein at least a portion of the stub is disposed on
the second region.
[0029] The first dielectric layer can comprise a ceramic material
having a plurality of voids, at least some of the voids filled with
magnetic particles. The magnetic particles can comprise
meta-materials. The second region underlying the stub preferably
includes magnetic particles.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 is a side view of a slot fed microstrip antenna
formed on a dielectric which includes a high dielectric region and
a low dielectric region, wherein the stub is disposed on the high
dielectric region, according to an embodiment of the invention.
[0031] FIG. 2 is a side view of the microstrip antenna shown in
FIG. 1, with added magnetic particles in the dielectric region
underlying the stub.
[0032] FIG. 3 is a side view of a slot fed microstrip patch antenna
which includes a first dielectric region including magnetic
particles disposed between the ground plane and the patch, and a
second dielectric region disposed between the ground plane and the
feed line which includes a high dielectric region underlying the
stub, the high dielectric region including magnetic particles,
according to another embodiment of the invention.
[0033] FIG. 4 is a flow chart that is useful for illustrating a
process for manufacturing a slot fed microstrip antenna of reduced
physical size and high radiation efficiency.
[0034] FIG. 5 is a side view of a slot fed microstrip antenna
formed on an antenna dielectric which includes magnetic particles,
the antenna providing impedance matching from the feed line into
the slot, the slot into the environment, and the slot into the
stub, according to an embodiment of the invention.
[0035] FIG. 6 is a side view of a slot fed microstrip patch antenna
formed on an antenna dielectric which includes magnetic particles,
the antenna providing impedance matching from the feed line into
the slot, and the slot to its interface with the antenna dielectric
beneath the patch and to the stub, according to an embodiment of
the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0036] Low dielectric constant board materials are ordinarily
selected for RF designs. For example, polytetrafluoroethylene
(PTFE) based composites such as RT/duroid.RTM. 6002 (dielectric
constant of 2.94; loss tangent of 0.0012) and RT/duroid.RTM. 5880
(dielectric constant of 2.2; loss tangent of 0.0007) are both
available from Rogers Microwave Products, Advanced Circuit
Materials Division, 100 S. Roosevelt Ave, Chandler, Ariz. 85226.
Both of these materials are common board material choices. The
above board materials provide are uniform across the board area in
terms of thickness and physical properties and provide dielectric
layers having relatively low dielectric constants with accompanying
low loss tangents. The relative permeability of both of these
materials is near 1.
[0037] Prior art antenna designs utilize mostly uniform dielectric
materials. Uniform dielectric properties necessarily compromise
antenna performance. A low dielectric constant substrate is
preferred for transmission lines due to loss considerations and for
antenna radiation efficiency, while a high dielectric constant
substrate is preferred to minimize the antenna size and optimize
energy coupling. Thus, inefficiencies and trade-offs necessarily
result in conventional slot fed microstrip antennas.
[0038] Even when separate substrates are used for the antenna and
the feed line, the uniform dielectric properties of each substrate
still generally compromises antenna performance. For example, a
substrate with a low dielectric constant in slot fed antennas
reduces the feed line loss but results in poor energy transfer
efficiency from the feed line through the slot due to the higher
dielectric constant in the slot region.
[0039] By comparison, the present invention provides the circuit
designer with an added level of flexibility by permitting the use
of dielectric layers, or portions thereof, with selectively
controlled dielectric constant and permeability properties which
can permit the circuit to be optimized to improve the efficiency,
the functionality and the physical profile of the antenna.
[0040] The dielectric regions may include magnetic particles to
impart a relative permeability in discrete substrate regions that
is not equal to one. In engineering applications, the permeability
is often expressed in relative, rather than in absolute, terms. The
relative permeability of a material in question is the ratio of the
material permeability to the permeability of free space, that is
.mu..sub.r=.mu./.mu..sub.0. The permeability of free space is
represented by the symbol .mu..sub.0 and it has a value of
1.257.times.10.sup.-6H/m.
[0041] Magnetic materials are materials having a relative
permeability .mu..sub.r either greater than 1, or less than 1.
Magnetic materials are commonly classified into the three groups
described below.
[0042] Diamagnetic materials are materials which have a relative
permeability of less than one, but typically from 0.99900 to
0.99999. For example, bismuth, lead, antimony, copper, zinc,
mercury, gold, and silver are known diamagnetic materials.
Accordingly, when subjected to a magnetic field, these materials
produce a slight decrease in the magnetic flux density as compared
to a vacuum.
[0043] Paramagnetic materials are materials which have a relative
permeability greater than one and up to about 10. Example of
paramagnetic materials are aluminum, platinum, manganese, and
chromium. Paramagnetic materials generally lose their magnetic
properties immediately after an external magnetic field is
removed.
[0044] Ferromagnetic materials are materials which provide a
relative permeability greater than 10. Ferromagnetic materials
include a variety of ferrites, iron, steel, nickel, cobalt, and
commercial alloys, such as alnico and peralloy. Ferrites, for
example, are made of ceramic material and have relative
permeabilities that range from about 50 to 200.
[0045] As used herein, the term "magnetic particles" refers to
particles when intermixed with dielectric materials, resulting in a
relative permeability .mu..sub.r greater than 1 for the dielectric
material. Accordingly, ferromagnetic and paramagnetic materials are
generally included in this definition, while diamagnetic particles
are generally not included. The relative permeability .mu..sub.r
can be provided in a large range depending on the intended
application, such as 1.1, 2, 3, 4, 6, 8, 10, 20, 30, 40, 50, 60,
80, 100, or higher, or values in between these values.
[0046] The tunable and localizable electric and magnetic properties
of the dielectric substrate may be realized by including
metamaterials in the dielectric substrate. The term "Metamaterials"
refers to composite materials formed from the mixing of two or more
different materials at a very fine level, such as the molecular or
nanometer level.
[0047] According to the present invention, a slot fed microstrip
antenna design is presented that has improved efficiency and
performance over prior art slot fed microstrip antenna designs. The
improvement results from enhancements including a stub which
improves coupling of electromagnetic energy between the feed line
and the slot. A dielectric layer disposed between the feed line and
the ground plane provides a first portion having a first dielectric
constant and at least a second portion having a second dielectric
constant. The second dielectric constant is higher as compared to
the first dielectric constant. At least a portion of the stub is
disposed on the high dielectric constant second portion. Portions
of the dielectric layer can include magnetic particles, preferably
including a dielectric region proximate to the stub to further
increase the efficiency and the overall performance of the slot
antenna.
[0048] Referring to FIG. 1, a side view of a slot fed microstrip
antenna 100 according to an embodiment of the invention is
presented. Antenna 100 includes a substrate dielectric layer 105.
Substrate layer 105 includes first dielectric region 112, second
dielectric region 113 (stub region), and third dielectric region
114 (dielectric junction region disposed between the feed line and
slot ). First dielectric region 112 has a relative permeability
.mu..sub.1 and relative permittivity (or dielectric constant)
.epsilon..sub.1, second dielectric region 113 has a relative
permeability of .mu..sub.2 and a relative permittivity of
.epsilon..sub.2, and third dielectric region 114 has a relative
permeability of .mu..sub.3 and a relative permittivity of
.epsilon..sub.3.
[0049] Ground plane 108 including slot 106 is disposed on
dielectric substrate 105. Antenna 100 can include an optional
dielectric cover disposed over ground plane 108 (not shown).
[0050] Feedline 117 is provided for transferring signal energy to
or from the slot. Feedline includes stub region 118. Feedline 117
may be a microstrip line or other suitable feed configuration and
may be driven by a variety of sources via a suitable connector and
interface.
[0051] Second dielectric region 113 has a higher relative
permittivity as compared to the relative permittivity in dielectric
region 112. For example, the relative permittivity in dielectric
region 112 can be 2 to 3, while the relative permittivity in
dielectric region 113 can be at least 4. For example, the relative
permittivity of dielectric region 113 can be 4, 6, 8,10, 20, 30,
40, 50, 60 or higher, or values in between these values.
[0052] Although ground plane 108 is shown as having a single slot
106, the invention is also compatible with multislot arrangements.
Multislot arrangements can be used to generate dual polarizations.
In addition, slots may generally be any shape that provides
adequate coupling between feed line 117 and slot 106, such as
rectangular or annular.
[0053] Third dielectric region 114 also preferably provides a
higher relative permittivity as compared to the relative
permittivity in dielectric region 112 to help concentrate the
electromagnetic fields in this region. The relative permittivity in
region 114 can be higher, lower, or equal to the relative
permittivity in region 113. In a preferred embodiment of the
invention, the intrinsic impedance of region 114 is selected to
match its environment. Assuming air is the environment, the
environment behaves like a vacuum. In that case,
.mu..sub.2=.epsilon..sub.2 will impedance match region 114 to the
environment.
[0054] Dielectric region 113 can also significantly influence the
electromagnetic fields radiated between feed line 117 and slot 106.
Careful selection of the dielectric region 113 material, size,
shape, and location can result in improved coupling between the
feed line 117 and the slot 106, even with substantial distances
therebetween.
[0055] Regarding the shape of dielectric region 113, region 113 can
be structured to be a column shape with a triangular or oval cross
section. In another embodiment, region 113 can be in the shape of a
cylinder.
[0056] In a preferred embodiment of the invention, the intrinsic
impedance of stub region 113 is selected to match the intrinsic
impedance of junction region 114. By matching the intrinsic
impedance of dielectric junction region 114 to the intrinsic
impedance of stub region 113, the radiation efficiency of antenna
100 is enhanced. Assuming the intrinsic impedance of region 114 is
selected to match air, .mu..sub.3 can be selected to equal
.epsilon..sub.3. Matching the intrinsic impedance of region 113 to
region 114 also reduces signal distortion and ringing which can be
significant problems which can arise from impedance mismatches into
the stub present in related art slot antennas.
[0057] In a preferred embodiment, dielectric region 113 includes a
plurality of magnetic particles disposed therein to provide a
relative permeability greater than 1. FIG. 2 shows antenna 200
which is identical to antenna 100 shown in FIG. 1, except a
plurality of magnetic particles 214 are provided in dielectric
region 113. Magnetic particles 214 can be metamaterial particles,
which can be inserted into voids created in substrate 105, such as
a ceramic substrate, as discussed in detail later. Magnetic
particles can provide dielectric substrate regions having
significant magnetic permeability. As used herein, significant
magnetic permeability refers to a relative magnetic permeability of
at least about 1.1. Conventional substrates materials have a
relative magnetic permeability of approximately 1. Using methods
described herein, .mu..sub.r can be provided in a wide range
depending on the intended application, such as 1.1, 2, 3, 4, 6, 8,
10, 20, 30, 40, 50, 60, 80, 100, or higher, or values in between
these values.
[0058] The invention can also be used to form slot fed microstrip
patch antennas having improved efficiency and performance. FIG. 3
shows patch antenna 300, the patch antenna 300 including at least
one patch radiator 309 and a second dielectric layer 305. The
structure below second dielectric layer 305 is the same as FIG. 1
and FIG. 2, except reference numbers have been renumbered as 300
series numbers.
[0059] A second dielectric layer is disposed between the ground
plane 308 and patch radiator 309. Second dielectric 305 comprises
first dielectric region 310 and second dielectric region 311, the
first region 310 preferably having a higher relative permittivity
as compared to second dielectric region 311. Region 310 also
preferably includes magnetic particles 314. Inclusion of magnetic
particles 314 permits region 310 to be impedance matched to
antenna's environment using a relative permeability equal to the
relative permittivity in region 310, to match to air. Thus, antenna
300 provides improved radiation efficiency by matching the
intrinsic impedance in region 310 (between slot 306 and patch 309)
and the intrinsic impedance of region 314 (between feed line 317
and slot 306).
[0060] For example, the relative permittivity in dielectric region
311 can be 2 to 3, while the relative permittivity in dielectric
region 310 can be at least 4. For example, the relative
permittivity of dielectric region 310 can be 4, 6, 8,10, 20, 30,
40, 50, 60 or higher, or values in between these values.
[0061] Antenna 300 achieves improved efficiency through enhanced
coupling of electromagnetic energy from feed line 317 through slot
306 to patch 309 through use of an improved stub 318. As discussed
earlier, improved stub 318 is provided through use of a high
permittivity substrate region proximate therein 313, which
preferably also includes optional magnetic particles 324. As noted
above, coupling efficiency is further improved through use
permittivity in dielectric region 313 which is proximate to stub
318 being higher than dielectric region 312.
[0062] Dielectric substrate boards having metamaterial portions
providing localized and selectable magnetic and dielectric
properties can be prepared as shown in FIG. 4 for use as customized
antenna substrates. In step 410, the dielectric board material can
be prepared. In step 420, at least a portion of the dielectric
board material can be differentially modified using meta-materials,
as described below, to reduce the physical size and achieve the
best possible efficiency for the antenna and associated circuitry.
The modification can include creating voids in a dielectric
material and filling some or substantially all of the voids with
magnetic particles. Finally, a metal layer can be applied to define
the conductive traces and surface areas associated with the antenna
elements and associated feed circuitry, such as the patch
radiators.
[0063] As defined herein, the term "meta-materials" refers to
composite materials formed from the mixing or arrangement of two or
more different materials at a very fine level, such as the angstrom
or nanometer level. Metamaterials allow tailoring of
electromagnetic properties of the composite, which can be defined
by effective dielectric constant (or relative permittivity) and the
effective relative permeability.
[0064] The process for preparing and modifying the dielectric board
material as described in steps 410 and 420 shall now be described
in some detail. It should be understood, however, that the methods
described herein are merely examples and the invention is not
intended to be so limited.
[0065] Appropriate bulk dielectric substrate materials can be
obtained from commercial materials manufacturers, such as DuPont
and Ferro. The unprocessed material, commonly called Green
Tape.TM., can be cut into sized portions from a bulk dielectric
tape, such as into 6 inch by 6 inch portions. For example, DuPont
Microcircuit Materials provides Green Tape material systems, such
as 951 Low-Temperature Cofire Dielectric Tape and Ferro Electronic
Materials ULF28-30 Ultra Low Fire COG dielectric formulation. These
substrate materials can be used to provide dielectric layers having
relatively moderate dielectric constants with accompanying
relatively low loss tangents for circuit operation at microwave
frequencies once fired.
[0066] In the process of creating a microwave circuit using
multiple sheets of dielectric substrate material, features such as
vias, voids, holes, or cavities can be punched through one or more
layers of tape. Voids can be defined using mechanical means (e.g.
punch) or directed energy means (e.g., laser drilling,
photolithography), but voids can also be defined using any other
suitable method. Some vias can reach through the entire thickness
of the sized substrate, while some voids can reach only through
varying portions of the substrate thickness.
[0067] The vias can then be filled with metal or other dielectric
or magnetic materials, or mixtures thereof, usually using stencils
for precise placement of the backfill materials. The individual
layers of tape can be stacked together in a conventional process to
produce a complete, multi-layer substrate. Alternatively,
individual layers of tape can be stacked together to produce an
incomplete, multi-layer substrate generally referred to as a
sub-stack.
[0068] Voided regions can also remain voids. If backfilled with
selected materials, the selected materials preferably include
metamaterials. The choice of a metamaterial composition can provide
tunable effective dielectric constants over a relatively continuous
range from 1 to about 2650. Tunable magnetic properties are also
available from certain metamaterials. For example, through choice
of suitable materials the relative effective magnetic permeability
generally can range from about 4 to 116 for most practical RF
applications. However, the relative effective magnetic permeability
can be as low as about 2 or reach into the thousands.
[0069] A given dielectric substrate may be differentially modified.
The term "differentially modified" as used herein refers to
modifications, including dopants, to a dielectric substrate layer
that result in at least one of the dielectric and magnetic
properties being different at one portion of the substrate as
compared to another portion. A differentially modified board
substrate preferably includes one or more metamaterial containing
regions. For example, the modification can be selective
modification where certain dielectric layer portions are modified
to produce a first set of dielectric or magnetic properties, while
other dielectric layer portions are modified differentially or left
unmodified to provide dielectric and/or magnetic properties
different from the first set of properties. Differential
modification can be accomplished in a variety of different
ways.
[0070] According to one embodiment, a supplemental dielectric layer
can be added to the dielectric layer. Techniques known in the art
such as various spray technologies, spin-on technologies, various
deposition technologies or sputtering can be used to apply the
supplemental dielectric layer. The supplemental dielectric layer
can be selectively added in localized regions, including inside
voids or holes, or over the entire existing dielectric layer. For
example, a supplemental dielectric layer can be used for providing
a substrate portion having an increased effective dielectric
constant. The dielectric material added as a supplemental layer can
include various polymeric materials.
[0071] The differential modifying step can further include locally
adding additional material to the dielectric layer or supplemental
dielectric layer. The addition of material can be used to further
control the effective dielectric constant or magnetic properties of
the dielectric layer to achieve a given design objective.
[0072] The additional material can include a plurality of metallic
and/or ceramic particles. Metal particles preferably include iron,
tungsten, cobalt, vanadium, manganese, certain rare-earth metals,
nickel or niobium particles. The particles are preferably nanometer
size particles, generally having sub-micron physical dimensions,
hereafter referred to as nanoparticles.
[0073] The particles, such as nanoparticles, can preferably be
organofunctionalized composite particles. For example,
organofunctionalized composite particles can include particles
having metallic cores with electrically insulating coatings or
electrically insulating cores with a metallic coating.
[0074] Magnetic metamaterial particles that are generally suitable
for controlling magnetic properties of dielectric layer for a
variety of applications described herein include ferrite
organoceramics (FexCyHz)-(Ca/Sr/Ba-Ceramic). These particles work
well for applications in the frequency range of 8-40 GHz.
Alternatively, or in addition thereto, niobium organoceramics
(NbCyHz)-(Ca/Sr/Ba-Ce-ramic) are useful for the frequency range of
12-40 GHz. The materials designated for high frequency are also
applicable to low frequency applications. These and other types of
composite particles can be obtained commercially.
[0075] In general, coated particles are preferable for use with the
present invention as they can aid in binding with a polymer matrix
or side chain moiety. In addition to controlling the magnetic
properties of the dielectric, the added particles can also be used
to control the effective dielectric constant of the material. Using
a fill ratio of composite particles from approximately 1to 70%, it
is possible to raise and possibly lower the dielectric constant of
substrate dielectric layer and/or supplemental dielectric layer
portions significantly. For example, adding organofunctionalized
nanoparticles to a dielectric layer can be used to raise the
dielectric constant of the modified dielectric layer portions.
[0076] Particles can be applied by a variety of techniques
including polyblending, mixing and filling with agitation. For
example, a dielectric constant may be raised from a value of 2 to
as high as 10 by using a variety of particles with a fill ratio of
up to about 70%. Metal oxides useful for this purpose can include
aluminum oxide, calcium oxide, magnesium oxide, nickel oxide,
zirconium oxide and niobium (II, IV and V) oxide. Lithium niobate
(LiNbO.sub.3), and zirconates, such as calcium zirconate and
magnesium zirconate, also may be used.
[0077] The selectable dielectric properties can be localized to
areas as small as about 10 nanometers, or cover large area regions,
including the entire board substrate surface. Conventional
techniques such as lithography and etching along with deposition
processing can be used for localized dielectric and magnetic
property manipulation.
[0078] Materials can be prepared mixed with other materials or
including varying densities of voided regions (which generally
introduce air) to produce effective dielectric constants in a
substantially continuous range from 2 to about 2650, as well as
other potentially desired substrate properties. For example,
materials exhibiting a low dielectric constant (<2 to about 4)
include silica with varying densities of voided regions. Alumina
with varying densities of voided regions can provide a dielectric
constant of about 4 to 9. Neither silica nor alumina have any
significant magnetic permeability. However, magnetic particles can
be added, such as up to 20 wt. %, to render these or any other
material significantly magnetic. For example, magnetic properties
may be tailored with organofunctionality. The impact on dielectric
constant from adding magnetic materials generally results in an
increase in the dielectric constant.
[0079] Medium dielectric constant materials generally have a range
from 70 to 500+/-10%. As noted above these materials may be mixed
with other materials or voids to provide desired effective
dielectric constant values. These materials can include ferrite
doped calcium titanate. Doping metals can include magnesium,
strontium and niobium. These materials have a range of 45 to 600 in
relative magnetic permeability.
[0080] For high dielectric constant applications, ferrite or
niobium doped calcium or barium titanate zirconates can be used.
These materials have a dielectric constant of about 2200 to 2650.
Doping percentages for these materials are generally from about 1
to 10%. As noted with respect to other materials, these materials
may be mixed with other materials or voids to provide desired
effective dielectric constant values.
[0081] These materials can generally be modified through various
molecular modification processing. Modification processing can
include void creation followed by filling with materials such as
carbon and fluorine based organo functional materials, such as
polytetrafluoroethylene PTFE.
[0082] Alternatively or in addition to organofunctional
integration, processing can include solid freeform fabrication
(SFF), photo, uv, x-ray, e-beam or ion-beam irradiation.
Lithography can also be performed using photo, uv, x-ray, e-beam or
ion-beam radiation.
[0083] Different materials, including metamaterials, can be applied
to different areas on substrate layers (sub-stacks), so that a
plurality of areas of the substrate layers (sub-stacks) have
different dielectric and/or magnetic properties. The backfill
materials, such as noted above, may be used in conjunction with one
or more additional processing steps to attain desired, dielectric
and/or magnetic properties, either locally or over a bulk substrate
portion.
[0084] A top layer conductor print is then generally applied to the
modified substrate layer, sub-stack, or complete stack. Conductor
traces can be provided using thin film techniques, thick film
techniques, electroplating or any other suitable technique. The
processes used to define the conductor pattern include, but are not
limited to standard lithography and stencil.
[0085] A base plate is then generally obtained for collating and
aligning a plurality of modified board substrates. Alignment holes
through each of the plurality of substrate boards can be used for
this purpose.
[0086] The plurality of layers of substrate, one or more
sub-stacks, or combination of layers and sub-stacks can then be
laminated (e.g. mechanically pressed) together using either
isostatic pressure, which puts pressure on the material from all
directions, or uniaxial pressure, which puts pressure on the
material from only one direction. The laminate substrate is then is
further processed as described above or placed into an oven to be
fired to a temperature suitable for the processed substrate
(approximately 850.degree. C. to 900.degree. C. for the materials
cited above).
[0087] The plurality of ceramic tape layers and stacked sub-stacks
of substrates can then be fired, using a suitable furnace that can
be controlled to rise in temperature at a rate suitable for the
substrate materials used. The process conditions used, such as the
rate of increase in temperature, final temperature, cool down
profile, and any necessary holds, are selected mindful of the
substrate material and any material backfilled therein or deposited
thereon. Following firing, stacked substrate boards, typically, are
inspected for flaws using an acoustic, optical, scanning electron,
or X-ray microscope.
[0088] The stacked ceramic substrates can then be optionally diced
into cingulated pieces as small as required to meet circuit
functional requirements. Following final inspection, the cingulated
substrate pieces can then be mounted to a test fixture for
evaluation of their various characteristics, such as to assure that
the dielectric, magnetic and/or electrical characteristics are
within specified limits.
[0089] Thus, dielectric substrate materials can be provided with
localized tunable dielectric and magnetic characteristics for
improving the density and performance of circuits, including those
comprising microstrip antennas, such as slot fed microstrip patch
antennas.
EXAMPLES
[0090] Several specific examples dealing with impedance matching
using dielectrics including magnetic particles according to the
invention is now presented. Impedance matching from the feed into
the slot, the slot into the stub, as well as the slot and the
environment (e.g. air) is demonstrated.
[0091] The condition necessary for having equal intrinsic
impedances at the interface between two different mediums, for a
normally incidence (.theta..sub.i=0.degree.) plane wave, is given
by 1 n n = m m .
[0092] This equation is used in order to obtain an impedance match
between the dielectric medium in the slot and the adjacent
dielectric medium, for example, an air environment (e.g. a slot
antenna with air above) or another dielectric (e.g. antenna
dielectric in the case of a patch antenna). The impedance match
into the environment is frequency independent. In many practical
applications, assuming that the angle of incidence is zero is a
generally reasonable approximation. However, when the angle of
incidence is substantially greater than zero, cosine terms should
be used along with the above equations in order to match the
intrinsic impedance of two mediums.
[0093] The materials considered are all assumed to be isotropic. A
computer program can be used to calculate these parameters.
However, since magnetic materials for microwave circuits have not
be used for matching the intrinsic impedance between two mediums
before the invention, no reliable software currently exists for
calculating the required material parameters necessary for
impedance matching.
[0094] The computations presented were simplified in order to
illustrate the physical principles involved. A more rigorous
approach, such as a finite element analysis can be used to model
the problems presented herein with additional accuracy.
Example 1
Slot with Air Above
[0095] Referring to FIG. 5, a slot antenna 500 is shown having air
(medium 1) above. Antenna 500 comprises transmission line 505 and
ground plane 510, the ground plane including slot 515. A dielectric
530 having a dielectric constant .epsilon..sub.r=7.8 is disposed
between transmission line 505 and ground plane 510 and comprises
region/medium 5, region/medium 4, region/medium 3 and region/medium
2. Region/medium 3 has an associated length (L) which is indicated
by reference 532. Stub region 540 of transmission line 505 is
disposed over region/medium 5. Region 525 which extends beyond stub
540 is assumed to have little bearing on this analysis and is thus
neglected.
[0096] The magnetic relative permeability values for medium 2 and 3
(.mu..sub.r.sub..sub.2 and .mu..sub.r.sub..sub.3) are determined by
using the condition for the intrinsic impedance matching of mediums
2 and 3. Specifically, the relative permeability
.mu..sub.r.sub..sub.2 of medium 2 is determined to permit the
matching of the intrinsic impedance of medium 2 to the intrinsic
impedance of medium 1 (the environment). Similarly, the relative
permeability .mu..sub.r.sub..sub.3 of medium 3 is determined to
permit the impedance matching of medium 2 to medium 4. In addition,
the length L of the matching section in medium 3 is determined in
order to match the intrinsic impedances of medium 2 and 4. The
length of L is a quarter of a wavelength at the selected frequency
of operation.
[0097] First, medium 1 and 2 are impedance matched to theoretically
eliminate the reflection coefficient at their interface using the
equation: 2 r 1 r 1 = r 2 r 2 ( 1 )
[0098] then the relative permeability for medium 2 is found as, 3 r
2 = r 1 r 2 r 1 = 1 7.8 1 r 2 = 7.8 ( 2 )
[0099] Thus, to match the slot into the environment (e.g. air) the
relative permeability .mu..sub.r.sub..sub.2 of medium (2) is
7.8.
[0100] Next, medium 4 can be impedance matched to medium 2. Medium
3 is used to match medium 2 to 4 using a length (L) of matching
section 532 in region 3 having an electrical length of a quarter
wavelength at a selected operating frequency, assumed to be 3 GHz.
Thus, matching section 432 functions as a quarter wave transformer.
To match medium 4 to medium 2, a quarter wave section 532 is
required to have an intrinsic impedance of:
.eta..sub.3={square root}{square root over
(.eta..sub.2.multidot..eta..sub- .4)} (3)
[0101] The intrinsic impedance for region 2 is: 4 2 = r 2 r 2 0 ( 4
)
[0102] where .eta..sub.0 is the intrinsic impedance of free space,
given by:
.eta..sub.0=120.pi..OMEGA..apprxeq.377.OMEGA. (5)
[0103] hence, the intrinsic impedance .eta..sub.2 of medium 2
becomes, 5 2 = 7.8 7.8 377 = 377 ( 6 )
[0104] The intrinsic impedance for region 4 is: 6 4 = r 4 r 4 0 = 1
7.8 377 135 ( 7 )
[0105] Substituting (0.7) and (0.6) in (0.3) gives the intrinsic
impedance for medium 3,
.eta..sub.3={square root}{square root over
(377.multidot.135)}.OMEGA.=225.- 6.OMEGA. (8)
[0106] Then, the relative permeability in medium 3 is found as: 7 3
= 225.6 = r 3 r 3 0 = r 3 7.8 377 r 3 = 7.8 ( 225.6 377 ) 2 = 2.79
( 9 )
[0107] The guided wavelength in medium 3 at 3 GHz, is given by 8 3
= c f 1 r 3 r 3 = 3 .times. 10 10 cm / s 3 .times. 10 9 Hz 1 7.8
2.79 = 2.14 cm ( 10 )
[0108] where c is the speed of light, and f is the frequency of
operation. Consequently, the length (L) of quarter wave matching
section 532 is given by 9 L = 3 4 = 2.14 4 cm = 0.536 cm ( 11 )
[0109] Note that the reactance between mediums (2) and (3) must be
zero, or very small, so that the impedance of medium (2) be matched
to the impedance of medium (4) using a quarter wave transformer
located in medium (3). This fact is well known in the theory of
quarter wave transformers.
[0110] Similarly, medium 5 can be impedance matched to medium 2. As
noted earlier, an improved stub 540 providing a high Q can permit
formation of a slot antenna having improved efficiency by disposing
stub 540 over a high dielectric constant medium/region 5 while also
impedance matching medium 5 to medium 2. Since region 2 is
impedance matched to air, region 5 should have a relative
permeability value that equals the dielectric constant value of
region/medium 5. For example, if .epsilon..sub.r=20, then
.mu..sub.r should be set to 20 as well.
Example 2
Slot with Dielectric Above, the Dielectric Having a Relative
Permeability of 1 and a Dielectric Constant of 10.
[0111] Referring to FIG. 6, a side view of a slot fed microstrip
patch antenna 600 is shown formed on an antenna dielectric 610
which provides a dielectric constant .epsilon..sub.r=10 and a
relative permeability .mu..sub.r=1. Antenna 600 includes the
microstrip patch antenna 615 and the ground plane 620. The ground
plane 620 includes a cutout region comprising a slot 625. The feed
line dielectric 630 is disposed between ground plane 620 and
microstrip feed line 605.
[0112] The feed line dielectric 630 comprises region/medium 5,
region/medium 4, region/medium 3 and region/medium 2. Region/medium
3 has an associated length (L) which is indicated by reference 632.
Stub region 640 of transmission line 605 is disposed over
region/medium 5. Region 635 which extends beyond stub 640 is
assumed to have little bearing on this analysis and is thus
neglected.
[0113] Since the relative permeability of the antenna dielectric is
equal to 1 and the dielectric constant is 10, the antenna
dielectric is clearly not matched to air as equal relative
permeability and dielectric constant, such as .mu..sub.r=10 and
.epsilon..sub.r=10 for the antenna dielectric would be required.
Although not demonstrated in this example, such a match can be
implemented using the invention. In this example, the relative
permeability for mediums 2 and 3 are calculated for optimum
impedance matching between mediums 2 and 4 as well as between
mediums 1 and 2. In addition, a length of the matching section in
medium 3 is then determined which has a length of a quarter
wavelength at a selected operating frequency. In this example, the
unknowns are again the relative permeability .mu..sub.r.sub..sub.2,
of medium 2, the relative permeability .mu..sub.r.sub..sub.3 of
medium 3 and L. First, using the equation 10 r 1 r 1 = r 2 r 2 ( 12
)
[0114] the relative permeability in medium 2 is: 11 r 2 = r 1 r 2 r
1 = 1 7.8 10 = 0.78 ( 13 )
[0115] In order to match medium 2 to medium 4, a quarter wave
section 632 is required with an intrinsic impedance of
.eta..sub.3={square root}{square root over
(.eta..sub.2.multidot..eta..sub- .4)} (14)
[0116] The intrinsic impedance for medium 2 is 12 2 = r 2 r 2 0 (
15 )
[0117] where .eta..sub.0 is the intrinsic impedance of free space,
given by
.eta..sub.0=120.pi..OMEGA..apprxeq.377.OMEGA. (16)
[0118] Hence, the intrinsic impedance .eta..sub.2 of medium 2
becomes, 13 2 = 0.78 7.8 377 = 119.2 ( 17 )
[0119] The intrinsic impedance for medium 4 is 14 4 = r 4 r 4 0 = 1
7.8 377 135 ( 18 )
[0120] Substituting (18) and (17) in (14) gives the intrinsic
impedance for medium 3 of
.eta..sub.3={square root}{square root over
(119.2.multidot.135)}.OMEGA.=12- 6.8.OMEGA. (19)
[0121] Then, the relative permeability for medium 3 is found as 15
3 = 126.8 = r 3 r 3 0 = r 3 7.8 377 r 3 = 7.8 ( 126.8 377 ) 2 =
0.8823 ( 20 )
[0122] The guided wavelength in medium (3), at 3 GHz, is given by
16 3 = c f 1 r 3 r 3 = 3 .times. 10 10 cm / s 3 .times. 10 9 Hz 1
7.8 0.8823 = 3.81 cm ( 21 )
[0123] where c is the speed of light and f is the frequency of
operation. Consequently, the length L is given by 17 L = 3 4 = 3.81
4 cm = 0.952 cm ( 22 )
[0124] As in example 1, the radiation efficiency of the antenna can
be further improved by matching the intrinsic impedance of medium 2
to the medium 5. This can be accomplished by setting the relative
permeability and dielectric constant values in medium/region 5 to
provide an intrinsic impedance which is impedance matched to
.eta..sub.2.
[0125] Since the relative permeability values required for
impedance matching in this example include values that are
substantially less than one, such matching will be difficult to
implement with existing materials. Therefore, the practical
implementation of this example will require the development of new
materials tailored specifically for this or similar applications
which require a medium having a relative permeability less than
1.
Example 3
Slot with Dielectric Above, that has a Relative Permeability of 10,
and a Dielectric Constant of 20.
[0126] This example is analogous to example 2, having the structure
shown in FIG. 6, except the dielectric constant .epsilon..sub.r of
the antenna dielectric 610 is 20 instead of 1. Since the relative
permeability of antenna dielectric 610 is equal to 10, and it is
different from its relative permittivity, antenna dielectric 610 is
again not matched to air. In this example, as in the previous
example, the permeability for mediums 2 and 3 for optimum impedance
matching between mediums 2 and 4 as well as for optimum impedance
matching between mediums 1 and 2 are calculated. In addition, a
length of the matching section in medium 3 is then determined which
has a length of a quarter wavelength at a selected operating
frequency. As before, the relative permeabilities
.mu..sub.r.sub..sub.2, of medium 2 and .mu..sub.r.sub..sub.3 of
medium 3, and the length L in medium 3 will be determined to match
the impedance of adjacent dielectric media.
[0127] First, using the equation 18 r 1 r 1 = r 2 r 2 ( 23 )
[0128] the relative permeability of medium 2 is found as, 19 r 2 =
r 1 r 2 r 1 = 10 7.8 20 = 3.9 ( 24 )
[0129] In order to match the impedance of medium 2 to medium 4, a
quarter wave section is required with an intrinsic impedance of
.eta..sub.3={square root}{square root over
(.eta..sub.2.multidot..eta..sub- .4)} (25)
[0130] The intrinsic impedance for medium 2 is 20 2 = r 2 r 2 0 (
26 )
[0131] where .eta..sub.0 is the intrinsic impedance of free space,
given by
.eta..sub.0=120.pi..OMEGA..apprxeq.377.OMEGA. (27)
[0132] hence, the intrinsic impedance of medium 2 .eta..sub.2
becomes, 21 2 = 3.9 7.8 377 = 266.58 ( 28 )
[0133] The intrinsic impedance for medium (4) is 22 4 = r 4 r 4 0 =
1 7.8 377 135 ( 29 )
[0134] Substituting (29) and (28) in (25) gives the intrinsic
impedance for medium 3, which is
.eta..sub.3={square root}{square root over
(266.58.multidot.135)}.OMEGA.=1- 89.7.OMEGA. (30)
[0135] Then, the relative permeability for medium (3) is found as
23 3 = 189.7 = r 3 r 3 0 = r 3 7.8 377 r 3 = 7.8 ( 189.7 377 ) 2 =
1.975 ( 31 )
[0136] The guided wavelength in medium 3, at 3 GHz, is given by 24
3 = c f 1 r 3 r 3 = 3 .times. 10 10 cm / s 3 .times. 10 9 Hz 1 7.8
1.975 = 2.548 cm ( 32 )
[0137] where c is the speed of light and f is the frequency of
operation. Consequently, the length 632 (L) is given by 25 L = 3 4
= 2.548 4 cm = 0.637 cm ( 33 )
[0138] As in examples 1 and 2, the radiation efficiency of the
antenna can be further improved by matching the intrinsic impedance
of medium 2 to the medium 5. This can be accomplished by setting
the relative permeability and dielectric constant values in
medium/region 5 to provide an intrinsic impedance which is
impedance matched to .eta..sub.2.
[0139] Comparing examples 2 and 3, through use of an antenna
dielectric 610 having a relative permeability substantially greater
than 1 facilitates impedance matching between mediums 1 and 2, as
well as between mediums 2 and 4 and 2 and 5, as the required
permeabilities for mediums 2 , 3 and 5 for matching these mediums
are both readily realizable as described herein.
[0140] While the preferred embodiments of the invention have been
illustrated and described, it will be clear that the invention is
not so limited. Numerous modifications, changes, variations,
substitutions and equivalents will occur to those skilled in the
art without departing from the spirit and scope of the present
invention as described in the claims.
* * * * *